Increasing Resource Efficiency in Waste Water Treatment Plants. Report No. 168

Wastewater treatment is a resource-intensive process that utilises several inputs, such as energy, chemicals and water, to produce an effluent that meets designated environmental standards. Driven by environmental regulations, the focus of wastewater treatment plants (WWTPs) has traditionally been the quality of the effluent and not necessarily the energy or resource effi- ciency of the plant. Regulations and penalties provide incentives to meet environmental effluent standards; however, to date, there are no such analogous pen- alties or incentives to expedite a focus on resource efficiency. It is imperative to recognise that resource utilisation and, indeed, sludge management also have significant environmental consequences, and therefore WWTP performance should be viewed holistically. This research sought to address this challenge by adopting a multi-pronged approach to audit and benchmark the resource efficiency of Irish WWTPs, including the use of life-cycle analysis (LCA) and exergy analysis. This study showed that the performance of WWTPs is a function of many variables, including some that the plant manager has little control over, such as influent concentrations and discharge requirements. Therefore, common, simple benchmarking metrics, such as kWh m3 or kWh PE, are unlikely to allow fair comparisons across plants. Similarly, energy audits or water quality testing alone are not sufficient for comprehensive audits and benchmarking plant performance. Effectiveness and efficiency should not be considered separately, and the ultimate goal should be to operate WWTPs that are both effective and efficient. In general, this is best achieved at the design phase, during which the longer term life-cycle costs and performance of the WWTP can be anticipated and optimised, rather than by solely focusing on the initial capital costs.